Wrought processing of brittle target alloy for sputtering applications

ABSTRACT

An ingot of material which is normally too brittle to allow successful rolling and wrought processing is formed so as to have a thickness-to-width ratio of less than about 0.5 and is annealed in a temperature range of 1000° F. to 2500° F. for a preselected time. The ingot is then rolled in a temperature range of 1500° F. to 2500° F. Additional/optional annealing of the resulting rolled plate in a temperature range of 500° F. to 2000° F., or between room temperature and 1500° F., and/or a final annealing between 500° F. and 1500° F., is possible. Sputtering targets are cut out of the rolled plate and used for the manufacture of storage disks.

This application is a Divisional of application Ser. No. 09/410,014filed Oct. 1, 1999.

FIELD OF THE INVENTION

This invention relates generally to multi-component cobalt alloymaterial which is used for sputter deposition of a magnetic layer on adata/storage disk, and more specifically to a method of producing analloy material, such as that based on a brittle Co-based alloy, whichexhibits microstructural and magnetic properties that are optimized formagnetron sputtering, and which finds application in the formation of asputtering target.

DESCRIPTION OF THE RELATED ART

The manufacture of storage disks and read/write heads involves the useof target materials that are used to sputter deposit a thin film mediaonto a suitable substrate. Cobalt-based alloy targets are frequentlyused for this purpose.

However, multi-component Co alloys with primary elemental additionssuch-as Cr, Pt, Ni (0 to 30 atomic%) and secondary elemental additionssuch as Ta, B, Nb, Sm, Fe, Si, Zr, W, Mo, V, Hf, and Ti (0 to 30atomic%) can be very difficult or impossible to conventionallyroll-process if the concentration of limited solid-solubility elementsis excessive. Since vacuum induction melting is necessary to ensure ahigh purity product, the only practical way to manufacture these brittlealloys has been to make as-cast targets. However, as cast targets haveseveral unfavorable microstructural characteristics such as largegrain-size, gross segregation of matrix and precipitate phases, throughthickness microstructural and chemical gradients and porosity.

It is fairly typical that a pair of magnetic alloy targets can be usedto fabricate in excess of 20,000 individual data-storage disks. Sincethe magnetic target alloy is continually loosing surface atomic layersduring the sputtering process, through thickness and in-plane targetmicrostructural homogeneity is essential to ensure film propertyhomogeneity on the many thousands of disks fabricated from each targetand the many thousand more fabricated from the numerous targetsconstituting a production lot or originating from several individualproduction lots. A production lot represents all the targets that areexposed to exactly the same thermomechanical history (i.e. originatingfrom one melted ingot).

Precipitate segregation in the matrix of Co-based magnetic target alloyshas been shown to impact deposited film magnetic properties such asCoercivity and Overwrite. When tens of thousands of data storage devicesare being made from several targets, it is necessary that the Coercivityresponse be consistent on all the disks, i.e., quality control, and notbe a function of the specific target utilized. Therefore, there is asubstantial need in the art for Co-based magnetic targets which exhibitconsistent performance, both within a target and from target to target.

Prior work serves to illustrate the effect of target precipitate andgrain uniformity on the sputter deposited film: Two targets of aCo—Cr—Ta alloy were fabricated. Target A was fabricated using standardtechniques and possessed a coarse and non-uniform Ta precipitate-phasemicrostructural morphology. Target B was fabricated to yield ahomogeneous microstructure consisting of a uniform dispersion of theprecipitate phase. Sputter process trials were in which the two targets,A and B, were placed on either side of the sputtering chamber so thatthey would be used for material deposition on the opposite sides of thesame disk. These precautions were taken to ensure that exactly the samesputter conditions and testing conditions applied for films depositedusing the two differently fabricated targets. Furthermore, targets A andB were interchanged in the sputtering chamber to ensure that noanomalies associated with location in the chamber were obscuring theresults of the investigation. The results of the analysis revealed thatthe magnetic films on disks fabricated using target A exhibitedcoercivities that ranged from 1580 Oersteds to 1780 Oersteds. Incontrast, the films on disks sputter deposited with magnetic materialusing target B exhibited Coercivities that ranged between 1920 to 2000Oersteds. The film Coercivity was ascertained using conventional VSMtesting techniques, widely employed in the disk manufacturing industry.There are several noteworthy points resulting from this analysis. First,target A, possessing a inhomogeneous microstructure, resulted in filmswith a significantly lower Coercivity response than films depositedusing target B which possessed a homogeneous microstructure. Second, theactual film Coercivities obtained from target A (overall range=200Oersteds) were,much less consistent than the film Coercivities obtainedfrom target B (overall range=80 Oersteds). These results demonstratethat if target precipitate and grain uniformity are not controlled, theresulting Coercivity response of the sputtered film can be diminishedand the disk-to-disk Coercivity consistency can be adversely effected.

Prior art which has been concerned with this or similar problems includethe following United States Patents:

U.S. Pat. No. Inventor Date of Patent 2,855,295 Hansel 1958 3,085,005Michael, et al. 1963 3,620,852 Herchenroeder et al. 1971 3,649,256Fletcher 1972 4,144,059 Liu et al. 1979 5,282,946 Kinoshita et al. 19945,334,267 Taniguchi et al. 1994 5,468,305 Uchida et al. 1995 5,728,279Schlott et al. 1998

Accordingly, there is a need in at least the data storage industry, fora technique by which targets made of Co-based alloys or the like, whichconventionally tend to exhibit brittleness to the degree that wroughtprocessing can not be used, can be manufactured with the requiredmicrostructurally homogeneous, fully dense and low permeabilitycharacteristics necessary to enable the production of high qualitystorage disks. The present invention meets this need.

SUMMARY OF THE INVENTION

An object of the present invention is therefore to provide a method offorming a piece of material suitable for making a magnetron sputteringtarget, that is capable of being rolled and wrought processed in amanner which improves the physical and magnetic characteristics such asgrain size, crystallographic texture, chemical/microstructuraluniformity and permeability.

A further object of the present invention is to enable the formation ofa sputtering target which is constituted in such a manner as to causethe magnetic layers which are sputter deposited onto the surface of adata/storage disk, to exhibit improved physical/magneticcharacteristics.

During efforts to overcome the above mentioned problem and to develop amicrostructurally homogeneous, fully dense and low permeability target,it was unexpectedly discovered that by subjecting cast ingots to anannealing step at temperatures between about 1500° F. and 2500° F., withor without the presence of an applied hydrostatic or compressivepressure, which can aid in stress assisted diffusional healing ofporosity, particularly good microstructures were obtained.

The annealing could be typically carried out for 0.5-168 hours. Whenpressure was applied, the pressures of 2 to 60 ksi were typically used.It was noted that the dimensions of an ingot treated in the abovemanner, had an effect on the final product and that a thickness-to-widthratio less than about 0.5 was favorable to facilitate a successfulconclusion to the rolling and wrought processing.

In brief, the above objects are thus achieved by forming an ingot ofmaterial which is normally too brittle to allow successful rolling andwrought processing so as to have a thickness-to-width ratio less thanabout 0.5, and annealing this ingot in a controlled temperatureenvironment of 1500° F. to 2500° F., and then rolling the annealedmember at an initial temperature range between 2500° F. and 1000° F.,reheating the ingot if the plate temperature falls below 500° F.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an SEM showing the effect of conventional wrought processingattempted on an ingot with more than the critical amount of limitedsolid-solubility elemental additives.

FIG. 2 is an SEM of a Co—18Cr—6Pt—6B alloy as-cast targetmicrostructure.

FIG. 3 is an EDS spectra of Co—18Cr—6Pt—6B: (a) matrix phase and (b)precipitate phase.

FIG. 4 is an SEM-BET micrograph of a Co—18Cr—6Pt—6B wrought-processedtarget microstructure using the process of the invention.

FIG. 5 shows the surface (a) and center (b) grain-size distributions forwrought processed Co—18Cr—6Pt—6B.

FIG. 6 shows the effect of target PTF on sputter process voltagestability and target lifetime.

FIG. 7 is an SEM micrograph of the microstructure of Co—15Cr—4Pt—5Ta—2Bas-cast target microstructure.

FIG. 8 is an Auger analysis which shows (a) the matrix phase, (b) thefirst precipitate phase and (c) the second precipitate phase of themicrostructure of FIG. 7.

FIG. 9 is an SEM-BEI micrograph showing Co—15Cr—4Pt—5Ta—2Bwrought-processed target microstructure using the invention.

FIG. 10 shows the surface (a) and center (b) grain-size distributionsfor wrought processed Co—15Cr—4Pt—5Ta—2B.

FIG. 11 shows SEM micrographs of the center and surface of as-casttarget microstructures of (a) Co—18Cr—6Pt—9B, (b) Co—12Cr—8Ta.

FIG. 12 is an SEM-BEI micrograph of wrought-processed targetmicrostructures using the invention for: (a) Co—18Cr—6Pt—9B, (b)Co—12Cr—8Ta.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Our research into Co—Cr—Pt—B—Ta alloys revealed an inhomogeneityassociated with as-cast microstructures in alloys wherein the solidsolubility of Ta and B in the Co matrix is less than 3 atomic% and 0.2atomic%, respectively. As more Ta and B are added to the matrix, thecontinuity (defined as the volume percent discontinuous intermetallicphases divided by the number of free nodes of these phases) of theintermetallic phases in the matrix increase. It was discovered thatbeyond a certain continuity, it was impossible to roll-deform theas-cast ingots due to the ease of crack propagation along the continuousand brittle intermetallic phase networks. This lead to ingots with ahigh elemental concentration fracturing during hot-rolling.

Nevertheless, our research demonstrated that if roll deformation can beapplied, the resulting microstructure develops a much more refined andhomogeneous morphology that greatly enhances the homogeneity of thesputter deposited films. For example, an as-cast product typically hasgrain and precipitate phase dimensions on the order of 200 microns and100 microns, respectively. In contrast, cast and wrought producttypically have grain and precipitate phase dimensions on the order of 20microns and 1 micron, respectively.

One approximation to determine how much brittle precipitate phase willform in a Co-base alloy, is to consider the sum of the individualelemental additions to Co normalized by their respective maximumsolid-solubilities in Co. Analysis of a range of different Co-basealloys demonstrated that, when (1) for Co based alloys with Cr content<25 atomic and the sum of solid solubility normalized elementaladditions to Co is greater than about 2, or (2) for Co based alloys withCr content >30 atomic% and the sum of solid solubility normalizedelemental additions to Co is greater than about 1, the alloy is notfabricable using standard wrought processing and targets have to bemanufactured using an as-cast technique (FIG. 1 is an illustration ofwhat happens when wrought processing is attempted on ingots with morethan the critical amount of limited solid-solubility elementaladditives). The table below illustrates this fact for the case themaximum solid solubilities of Cr, Pt, Ta and B are approximately 40,100, 4 and 0.2 atomic%, respectively.

Sum of Normalized Std. Wrought Alloy Cr (at %) Solid SolubilitiesProcessing Co-12Cr-8Ta <25 2.3 No Co-16Cr-10Pt-6B-4Ta <25 31.4 NoCo-10Cr-4Ta <25 1.3 Yes Co-19Cr-3Pt-4Ta <25 1.5 Yes Co-40Cr-10Ru >25 1.6No Co-35Cr-6Ti >25 1.3 No Co-45Cr >25 1.1 No Co37Cr >25 0.9 Yes

It is noteworthy that when the sum of solid solubility normalizedelemental additions to Co, is less than critical values stated in thepreceding paragraphs, the invention described herein can still beapplied to achieve more aggressive wrought processing (to promotegreater microstructural homogeneity) than achievable throughconventional processing.

In brief, rolling of cast ingots is an essential process step forproducing microstructurally homogeneous, fully dense and lowpermeability targets for magnetron sputtering applications.Unfortunately, until now, the use of as-cast targets has been the onlyprocess option for several brittle Co-base alloys used in thedata-storage industry.

In accordance with the present invention, microstructural evaluationafter annealing of the brittle ingots revealed that, in addition topartial healing of internal porosity, the process can promote a staticrecrystallization of the microstructure. It was also shown that theas-cast grain-size can be reduced from several hundred microns aftercasting to less than 100 microns with the application of the annealingtreatment described above. In further experimentation carried out onpieces of annealed cast ingots, it was shown that success in wroughtprocessing brittle ingots subject to a post casting annealing treatmentwas possible. Specifically, a plate that was machined to process a lowthickness to width ratio was particularly forgiving to roll processing.Based on these results, further investigation revealed that brittleCo-base alloys that to this point could not be rolled, can be wroughtprocessed under the following conditions.

1. An ingot is annealed after casting with or without the presence of anapplied pressure or compressive stress. In its simplest and mostpractical form, this annealing can be facilitated by slow cooling theingot after casting (cooling rate less than or equal to air cooling).

2. The ingot is cast or machined to have a thickness-to-width ratio lessthan approximately 0.5. Therefore, if an ingot is 7″ wide, then thethickness prior to wrought deformation should be less than about 3.5″.

In order to obtain an optimum microstructure for sputtering, theannealed ingot with a thickness-to-width aspect ratio less than approx.0.5, should be rolled at temperatures between 1000° F. to 2500° F., topromote maximum densification and a fine graineddynamically-recrystallized microstructure mechanically. homogenized (viashear deformation) to ensure a fine homogeneous distribution of theprecipitate phase(s).

More specifically, a first aspect of the invention resides in a methodof producing an alloy member from which sputtering targets can beformed, comprising the steps of: annealing an ingot of an alloy at 1500°F. to 2500° F. for a predetermined time; adjusting the ingot to possessa thickness-to-width aspect ratio of less than 0.5; and rolling theingot between 1000° F. to 2500° F. to produce the member in the form ofa rolled plate.

In accordance with this aspect the predetermined time is in a range of0.5-168 hours. Further, the method can optionally include one or morethe of the steps of: annealing the rolled plate at a temperature ofbetween 500° F. and 2000° F.; annealing the rolled plate at atemperature of between 500° F. and 2000° F. and introducing subsequentrolling steps at temperatures below 1500° F. These additional steps areexpressly added to further aid in promoting microstructural homogeneityvia recrystallization and shear deformation processes. Further inaccordance with this aspect of the invention, the method is such thatthe alloy contains cobalt and elemental additions, the sum of the solidsolubility of normalized elemental additions being greater than apredetermined number, which is greater than 1, or alternatively in therange of 1-50. As previously mentioned, in cases when the sum of solidsolubility normalized elemental additions to Co, is less than 1, theinvention described herein can still be applied to achieve moreaggressive wrought processing (to promote greater microstructuralhomogeneity) than achievable through conventional processing.

As will be clearly appreciated, the present invention is based on anovel fabrication technique for brittle Co-base alloys which can promotespecific product microstructural and magnetic properties which areoptimum for magnetron sputtering. The process according to the presentinvention, is applicable to brittle Co-base alloys where the sum ofsolid solubility normalized elemental additions to Co exceeds betweenabout 1. The elemental additions are, but not limited to, Cr, Pt, Ni,Ta, B, Nb, Ru, Rh, Sm, Fe, Si, Zr, W, Mo, C, O, V, Hf, and Ti. Theprocess according to the present invention is applicable to all classesof brittle alloys, not just Co-based types.

More specifically, the process which characterizes the present inventionfeatures the steps of:

casting an ingot;

annealing the ingot at a temperature of between 1500° F. to 2500° F.(for 0.5 to 168 hours), with or without the presence of an appliedhydrostatic or compressive pressure (typical pressures of 2 to 60 ksican be used);

adjusting the ingot to possess a thickness-to-width aspect ratio of lessthan 0.5; and

rolling the ingot at an initial temperature of between 1000° F. to 2500°F. and reheating the ingot if the temperature falls below 500° F.

In accordance with the present invention, further features include theoptions of annealing the rolled plates at temperatures between 500° F.and 2000° F.; or annealing the plates at temperatures between roomtemperature and 1500° F.; annealing the rolled plate at a temperature ofbetween 500° F. and 2000° F. and introducing subsequent rolling steps attemperatures below 1500° F.; or effecting a final annealing attemperatures between 500° F. and 1500° F.

The properties which are produced in accordance with the processaccording to the present invention are:

Average product grain-size of less than 100 microns.

Average product precipitate dimension of less than 50 microns.

No significant through thickness grain-size and precipitate sizegradients.

Theoretical densification attained.

Product PTF greater than 20%.

PTF of a magnetic target is defined as the ratio of transmitted magneticfield to applied magnetic field. A PTF value of 100% is indicative of anon-magnetic material where none of the applied field is shunted throughthe bulk of the target.

PTF of magnetic target materials is typically specified in the range of0 to 100%, with the majority of commercially produced materialsexhibiting values between 10 to 95%. There are several differenttechniques that are commonly utilized to measure product PTF. One of themost prevalent techniques utilized involves placing a 4.4 (+/−0.4)kilogauss bar magnet in contact on one side of the target material andmonitoring the transmitted field using a axial Hall probe in contact onthe other side of the target material. The maximum value of the magneticfield transmitted field through the bulk of the target divided by theapplied field strength in the absence of the target between the magnetand probe (maintained at the same distance apart as when the target wasbetween them) is defined as the pass through flux (PTF). PTF can beexpressed as either a fraction or a percent. It is well established inthe prior art that increasing target material PTF promotes a less severeerosion profile which enhances target material utilization andsubsequently contributes to a reduction in cost from the usersviewpoint. The presence of severe target erosion profiles also promotesa point source sputtering phenomena which can result in less thanoptimum deposited film thickness uniformity. Therefore, increasingtarget material PTF has the added benefit of increasing deposited filmthickness uniformity

The following examples are presented to illustrate the invention but theinvention is not to be considered as limited thereto.

EXAMPLE 1

An alloy containing Co—18Cr—6Pt—6B was heated via induction under avacuum of between 10 to 40 milliTorr until molten and cast to form aningot with a thickness-to-width aspect ratio between 0.3 to 0.5. Thetemperature of the ingot was allowed to reduce in a controlled fashionfor a period of 2 hours until a temperature of 1500° F. was reached. Theingot was subsequently annealed between 2000° F. to 2500° F. for 10hours and hot-rolled in that range for a total reduction of 80%. Afterrolling the ingot was given a second-stage anneal between 1000° F. to1800° F. for 3 hours and rolled in that range for a further 20%reduction.

FIG. 2 is an Scanning Electron Microscope (SEM) micrograph using BackScattered Electron Imaging (BEI) depicting the microstructure of theingot and resultant as-cast targets manufactured using conventionalparadigms. EDS (FIG. 3) and Auger analysis confirm that the matrix phase(light appearing phase) is composed of Co, Cr and Pt and that theprecipitate phase (dark appearing phase) has the approximate compositionCo₃Cr₂B. The average grain-size and precipitate thickness determinedusing standard ASTM metallographic techniques outlined in “QuantitativeMetallography” by E. E. Underwood, ASM Handbook. Vol. 9, are 140 and 90micrometers, respectively. The PTF of the as-cast product ranges isnominally about 15% This value is low and represents a sub-optimumsituation as far as target utilization during sputtering is concerned.

In contrast, FIG. 4 is an SEM-BEI micrograph illustrating themicrostructural benefits of applying the novel process described hereinto the Co—18Cr—6Pt—6B alloy. The phase compositions are similar to thosedetermined in the as-cast state, but the morphology is very different asa result of the wrought processing employed. The average grain-size andprecipitate are 13 and 1 micrometers, respectively. The microstructureis very uniform, and this uniformity persists through the thickness ofthe target product. FIG. 5 depicts the surface and center grain-sizedistributions illustrating that no statistically significant differenceexists through the thickness of the product. As mentioned in theBackground, A fine-grain/fine-precipitate microstructure and throughthickness uniformity is critical to ensure consistent target performancesince 1 target pair can typically be utilized to manufacture in excessof 20,000 storage media disks.

Furthermore, application of the proprietary wrought process described inthe present patent raises the product PTF from 15% as-cast toapproximately 75%. This more than four-fold improvement in product PTFhas a significant impact in rendering the sputter process more stableand extending the useful life of the target product. To illustrate theimpact of high PTF, FIG. 6 demonstrates the positive effect of raisingnominal target PTF from 65% to 75% on improving sputter process firingvoltage stability and target life time. Clearly, increasing PTF from 15%to 75% will have a profound effect on sputter process stability andtarget yield.

In summary, application of the new proprietary wrought process toCo—18Cr—6Pt—6B yielded significant microstructural uniformity and PTFimprovements over conventionally fabricated as-cast product. Thefollowing examples will serve to establish the generality of the novelparadigms developed in the present patent.

EXAMPLE 2

An alloy containing Co—15Cr—4Pt—5Ta—2B was heated via induction under avacuum of between 10 to 40 milliTorr until molten and cast to form aningot with a thickness-to-width aspect ratio between 0.1 to 0.3. Thetemperature of the ingot was allowed to reduce in a controlled fashionfor a period of 1 hours until a temperature of 1000° F. was reached. Theingot was subsequently annealed between 2000° F. to 2500° F. for 10hours and hot-rolled between 1200° F. to 2100° F. for a total reductionof 50% and allowed to cool in a controlled fashion from the rolling,temperature to 300° F. in 6 hours.

FIG. 7 is a Scanning Electron Microscope (SEM) micrograph using BackScattered Electron Imaging (BEI) depicting the microstructure of theingot and resultant as-cast targets manufactured using conventionalparadigms. EDS (FIG. 8) and Auger analysis confirm that the matrix phase(gray appearing phase) is composed of Co, Cr, Pt and Ta, that the firstprecipitate phase (light appearing phase) is composed of Co, Pt and Taand the second precipitate phase (dark appearing phase) is composed ofCo, Cr, Ta and B. The average grain-size and precipitate diameter are180 and 85 micrometers, respectively. The PTF of the as-cast productranges is nominally about 10%. This value is even lower than thatobtained in the case of as-cast Co—18Cr—6Pt—6B.

In contrast, FIG. 9 is an SEM-BEI micrograph illustrating the uniformmicrostructure obtained by applying the novel process described hereinto the Co—15Cr—4Pt—5Ta—2B alloy. The phase compositions are similar tothose determined in the as-cast state, but the morphology is verydifferent as a result of the wrought processing employed. The averagegrain-size and precipitate dimension are 14 and 1 micrometers,respectively. The microstructure is very uniform, and this uniformitypersists through the thickness of the target product. FIG. 10 depictsthe surface and center grain-size distributions illustrating that nostatistically significant difference exists through the thickness of theproduct.

As in the previous example, application of the proprietary wroughtprocess described in the present patent raises the product PTF from 10%as-cast to approximately 90%. This represents a very significantnine-fold improvement in product PTF. Once again, it is clear thatapplication of the proprietary wrought process described herein tocomplex, brittle and multi-phasic alloys can have a significant positiveimpact on microstructural homogeneity and macromagnetic (PTF)properties.

EXAMPLE 3

Two alloys, Co—18Cr—6Pt—9B and Co—12Cr—8Ta were heated via inductionunder a vacuum of between 10 to 40 milliTorr until molten and cast toform ingots with thickness-to-width aspect ratios of 0.4, 0.25 and 0.07,respectively. The temperature of the ingots were allowed to reduce in acontrolled fashion for a period of 1.5 hours until a temperature of1000° F. was reached. All the ingots was subsequently annealed between2000° F. to 2500° F. for between 6 to 15 hours and hot-rolled between1800° F. to 2500° F. for a total reduction of 50% and allowed to cool ina controlled fashion from the rolling temperature to 200° F. in 2 hours.

FIG. 11 illustrates Scanning Electron Microscope (SEM) micrographs usingBack Scattered Electron Imaging (BEI) depicting the microstructure ofthe ingots and resultant as-cast targets manufactured using conventionalparadigms. SEM-EDS and Auger analysis confirm the following phasecompositions for the different alloys:

Co-18Cr-6Pt-9B: matrix phase (light) Co-Cr-Pt Precipitate phase (dark)Co-Cr-B Co-12Cr-8Ta matrix phase (dark) Co-Cr-Ta Precipitate phase(light) Co-Ta

The average as-cast grain-size, precipitate diameters and PTF are

Co-18Cr-6Pt-9B: 130 and 135 micrometers and 8% Co-12Cr-8Ta 185 and 170micrometers and 25%

In contrast, FIG. 12 is an SEM-BEI micrograph illustrating the uniformmicrostructure obtained by applying the novel process described herein.The phase compositions are similar to those determined in the as-castconventional state, but the morphology is very different as a result ofthe wrought processing employed. The average grain-size and precipitatediameters after application of the novel processing described hereinare:

Co-18Cr-6Pt-9B: 9 and 1 micrometers Co-12Cr-8Ta 35 and 40 micrometers

As in the previous examples, the microstructure is very uniform, andthis uniformity persists through the thickness of the target product forall three of the alloys listed above.

Application of the proprietary wrought process described in the presentpatent raises Co—18Cr6Pt—9B and Co—12Cr—8Ta product PTF from 8% and 25%.respectively, as-cast to approximately 80% and 95%, respectively. It isgenerally understood that in Co-based alloys, if the combined content ofCr, Ta, Nb and W exceed approximately 25 atomic%, then the alloy isparamagnetic at ambient temperatures and the room temperature PTF is100%. This is the case for alloys such as Co—40Cr—(Ti,Al,Ru). For thesetypes of alloys, the main benefit of the proprietary wrought processdescribed in the present patent is to promote microstructural refinementand homogeneity for more uniform sputter processing and thin film mediaperformance.

It will be appreciated that although the invention has been disclosedwith reference to only a limited number of embodiments and examples,that the invention is not so limited and is bound only by the scope ofthe appended claims.

What is claimed is:
 1. A method for producing an alloy membercharacterized by a substantially microstructurally homogeneousmorphology and magnetic properties optimized for forming lowpermeability sputtering targets therefrom, the alloy member having grainuniformity comprising an average grain size of less than 100 microns,and an average product precipitate dimension of less than 50 microns,the method comprising: a) providing an alloy which is sufficientlybrittle that the alloy cannot be rolled and wrought processed to form aproduct having a substantially homogenous morphology; b) casting thealloy as an ingot; c) annealing the ingot by heating at a temperature ofbetween 1500° F. and 2500° F.; d) working the annealed ingot to form analloy member which has a thickness to width ratio of less thanapproximately 0.5; and e) rolling the alloy member at a temperature ofbetween 1000° F. and 2500° F. to produce the member in the form of arolled plate and promote densification and fine grain in the alloymember.
 2. A method according to claim 1, wherein the annealing step isconducted at atmospheric pressure.
 3. A method according to claim 1,wherein the annealing step is conducted at under a pressure of 2 to 60ksi.
 4. A method according to claim 1, wherein after the annealing step,the ingot is cooled at a rate of less than or equal to air cooling.
 5. Amethod according to claim 1, wherein the alloy is a brittle cobalt basedalloy wherein elemental additions to the cobalt alloy are ininsufficient amounts to produce intermetallic phases which interferewith the homogeneous nature of the alloy.
 6. A method according to claim5, wherein the cobalt based alloy comprises elemental additions of amember selected from the group consisting of Cr, Pt, Ni, Ta, B, Nb, Ru,Rh, Sm, Fe, Si, Zr, W, Mo, C, O, V, Hf, Ti and mixtures thereof.
 7. Amethod according to claim 5, wherein the brittle alloy is aCo—Cr—Pt—B—Ta alloy.
 8. A method according to claim 6, wherein thebrittle alloy is selected from the group consisting of: Co—12Cr—8 TaCo—18Cr—6Pt—6B Co—15Cr—4Pt—5Ta—2bf Co—16Cr—10Pt—6B—4Ta Co—10Cr—4TaCo—19Cr—3Pt—4Ta Co—40Cr—10Ru Co—35Cr—6Ti Co—45Cr Co—37Cr all amountsexpressed in atomic %.
 9. A method as set forth in claim 1, whereinannealing is carried out for a time period of about 0.5-168 hours.
 10. Amethod as set forth in claim 1, comprising the further step of (f) ofannealing the rolled plate at a temperature of between 500° F. and 2000°F.
 11. A method as set forth in claim 1, comprising the further step of:annealing the rolled plate between room temperature and a temperature of1500° F.
 12. A method as set forth in claim 1, comprising the furthersteps of: cutting a sputtering target from the rolled plate; andannealing the target at a temperature of between 500° F. and 1500° F.13. A method as set forth in claim 1, comprising the further steps of:cutting a sputtering target out of the rolled plate; and annealing thetarget at a temperature of 500° F. and 1500° F. and subsequently rollingthe annealed target at temperatures below 1500° F.
 14. A method as setforth in claim 1, wherein the alloy contains cobalt and elementaladditions, the sum of the solid solubility of normalized elementaladditions being greater than one.
 15. A method as set forth in claim 13,wherein the annealing is for greater than about 1 hour.
 16. A method asset forth in claim 13, wherein the annealing time is within the range of10-40 hours.
 17. A method as set forth in claim 1, wherein the alloy isCo—18Cr—6Pt—6B expressed in atomic %.
 18. A method as set forth in claim1, wherein the alloy is Co—15Cr—4Pt—5Ta—2B expressed in atomic %.
 19. Amethod as set forth in claim 1, wherein the alloy is Co—18Cr—6Pt—9Bexpressed in atomic %.
 20. A method as set forth in claim 1, wherein thealloy is Co—12Cr—8Ta expressed in atomic %.